Things were very expensive those days.You_______ a very good dinner if you only paid 10.     A.can't have   B.may have  C.can't  have had   D.may have hadIs it ___ that professor Black will come to visit China again?  A.sure   B.certain   C.really  D.truly

第一题 A 因为只付十元 所以不可能很好 应用否定 而C can 后面加动词原形 不加完成时
第二题 B 改成陈述句是 That professor Black will come to visit China again is certain. is 后面加形容词 先排除 C D 再从意思上分析 选 B

答案 C B

2 选B certain
Sure与certain是近义词,均作“一定的,确信的”等解.两者用法相似,多数情况下可换用,但有时不能换用.
在“It is…that结构中只能用certain,不能用sure.例如：
It is certain that he will come. 毫无疑问他会来
It was certain that our football team would win the game. 我们的足球队无疑会赢得比赛
如是否定句,用whether,不同that.例如：
It is not certain whether he will come. 他来不来还不一定.
题目疑问句,同理 教授确定还会再来中国吗?
1 选C
can/could + have + 过去分词
表示对过去某种情况怀疑或者不确定
can和could一般用于否定句和疑问句,could语气较弱
例句
He can't have finished the work so soon
他不可能这么快完成工作
I didn't see her at the meeting this morning；she can't/couldn't have spoken at the meeting
今天早上我没看到她出席会议,她不可能在会上发过言.
题目 那些日子物价很高,你只花10块钱是不可能吃到什么好东西的

这些天东西都很贵，你 一顿好的晚餐如果你付出10元。
那个教授是要再一次来中国玩吗